(1) Field of the Invention
The present invention relates generally to environmental control systems and, more particularly, to a system for the control of volatile organic compounds ("VOC's") and other substances in a spray booth.
(2) Description of the Prior Art
Industry is becoming more sensitive to the effects of long-term exposure to VOC's. Recently, the Occupational Safety and Health Administration (OSHA) has amended the existing air contaminant standard to lower the permissible exposure limit (PEL) on over 400 substances and has added 164 substances not previously regulated. For example, among solvents, the PEL for Toluene was set at 100 parts per million (ppm) and the short-term exposure limit (STEL) was set at 150 ppm. Similar limits have been set for other solvents.
There are several engineering approaches to reducing PEL's. One is to improve ventilation by increasing the amount of fresh air being brought into an area. Good capture results can be achieved by using a large quantity of air to deal with a relatively small quantity of VOC's. Unfortunately, this is an expensive operation and not practical for most manufacturing situations. Another option is isolation. For example, walls, partitions and curtains may be designed to separate personnel from hazardous fumes.
Particularly troublesome are vapors emitted from paint and finish-spraying processes utilized, for example, in the automobile and furniture industry. The articles to be painted and finished are confined in a small, enclosed area and operators must spray numerous coats of various surface coverings over a short period of time. As these coatings are applied, vapors arise from the drying process and need to be evacuated from the working area as quickly as possible.
U.S. Pat. No 5,133,246, issued to Campbell, discloses a control system for controlling, capturing and disposal of VOC's and other substances that includes a spray booth having an entrance, an exit and an accessible working area in one or more areas adjacent to the working area which uses high velocity air currents to provide invadable spray booth sealing enclosures at the entrance, exit, working, and adjacent areas. An interior air flow supply means directs air generally in the direction of the article to be sprayed to move the floating particles of vapors and an air evacuation means recycles the supply air and removes the VOC's and other substances entrained therein to remote locations. However, the high velocities associated with an air curtain causes a vacuum near the air curtain nozzle which tends to infuse VOC's from the surrounding area and expose the personnel thereto.
U.S Pat. Nos. 4,237,780 and 5,127,574, issued to Truhan and Mosser et al., respectively, both disclose spray booths having vertical ventilation systems. However, these systems are high-velocity, high-CFM systems, which are expensive to manufacture and operate and which may disrupt the spray pattern from the spray gun.
Thus, there remains the need for a new and improved spray booth which requires significantly lower air flow than conventional systems while, at the same time, supplying superior control of VOC's in the area of the operator.